1. Field of the Invention
The present invention relates to compositions of polyolefin and polyvinyl alcohol which can be utilized in forming a multi layer article, and to a film, a sheet and a processed article having excellent barrier properties against gases and organic solvents. More specifically, the present invention relates to compositions which are prepared by adding a prescribed amount of a compatibilizer, an initiator, a plasticizer, a processing aid and antioxidant into polyolefin and polyvinyl alcohol, and to a film, a sheet, a processed article or a multi layer product manufactured with the composition by conventional melt processing methods. The resulting melt extruded pellets form a unique morphology which exhibits all of the properties of each polymer existing in the composition.
2. Background of the Invention
Polyvinyl alcohol is known to have excellent barrier properties against gases and organic solvents. However, methods for manufacturing products by using polyvinyl alcohol have been greatly limited due to many processing problems. To solve these problems, the blending or the modification with other polymers has been attempted. However, it is very difficult to manufacture a composition which can be melt-processed by a conventional thermoplastic-processing method and sufficiently retain the excellent barrier properties of polyvinyl alcohol in the products.
For these reasons, in the prior art, the mixture of polyolefin and polyvinyl alcohol was generally used in the field using hydrophilic properties of polyvinyl alcohol rather than in the field of multi layer products having barrier properties. As such an example, the mixture of polyolefin and polyvinyl alcohol has been used either to manufacture electrically conductive plastic articles or as a drying agent for batteries. The mixture has been mainly used as a sizing agent for fibers or paper surfaces and adhesives (paper, plywood, non-woven fabric, etc.). It has been also used as a reinforcing fiber to enhance the strength of cement or as a dispersing stabilizer in emulsion polymerization.
To utilize the excellent barrier properties of polyvinyl alcohol against gases and organic solvents, the techniques wherein polyvinyl alcohol is melted and then processed to form a film have been reported in numerous patents. In the following, we will summarize the content of several patents; however, it should be noted that all methods set forth below do not necessarily make it possible to melt polyvinyl alcohol completely for it to be processed into articles freely. Furthermore, the methods are far from utilizing the excellent barrier properties of polyvinyl alcohol against gases and organic solvents to an extent which would achieve marketability.
U.S. Pat. No. 3,365,413 discloses an invention using polyvinyl alcohol in a blow extrusion. In the invention, the inventor made acetate to work as a plasticizer by keeping the content of acetate from 25 to 40% by weight in the polymerization of polyvinyl alcohol and lowered the melting point of resin.
U.S. Pat. No. 3,997,489 discloses a method for improving melt processing properties by adding low molecular weight oil or wax. U.S Pat. No. 4,206,101 discloses soluble films which are rapidly and completely soluble in water by melt extrusion using 5 to 20 parts by weight of a polyethylene glycol in 100 parts by weight of a polyvinyl alcohol.
U.S. Pat. No. 4,244,914 discloses a process for plasticizing polyvinyl alcohol with water, and heating under pressure to bring it to the prastisol state, removing the created vapors using an extruder vent, and preparing coextruded multi layer articles. U.S. Pat. No. 4,611,019 discloses a melt extrudable composition by adding polyvinylamide or polyester as a plasticizer into a polyvinyl alcohol.
U.S. Pat. No. 4,672,082 provides a method for producing articles made from polyvinyl alcohol in the state of substantially water-free non-hydroxyl plasticizer but it has a problem in that the cooling rate must be sufficiently slowed to improve the barrier property.
U.S. Pat. No. 5,317,052 discloses a technology which makes melting process possible by adding a metal compound to polyvinyl alcohol and thus raising its thermal decomposition temperature. European Patent 0 415 357 and U.S. Pat. No. 5,051,222 provide a method for producing gel-free thermoplastic polyvinyl alcohol by remodeling an extruder and providing polyvinyl alcohol with enough energy to rapidly melt the polyvinyl alcohol and substantially eliminate the crystallinity in the polyvinyl alcohol melt.
European Patent 0 187 040 discloses a method for producing films by introducing polyvinyl alcohol into polyethylene using silane or alkoxysilane as a compatibilizer to form an olefin/vinyl alcohol segment copolymer. However, when compared with the present invention, this method has several differences:
(1) a plasticizer, a processing aid and an antioxidant are not used in the modification of polyvinyl alcohol,
(2) only limited kinds of compatibilizer are used, and
(3) the barrier property against oxygen is significantly detericrated in spite of using the same amount of polyvinyl alcohol as the present invention.
This is because the patent only made possible the blending of polyolefin and polyvinyl alcohol using silane without improving the melting property of polyvinyl alcohol. Therefore, the obtained olefin/vinyl alcohol segment copolymer does not have the uiique morphology of the mixture consisting of polyolefin and polyvinyl alcohol as provided by the present invention, and thus the exhibition of the barrier properties of polyvinyl alcohol is limited.
European Patent 0 152 180 discloses a method for grafting polyvinyl alcohol by introducing a functional group into polyolefin. However, it chiefly deals with the properties of a compatibilizer and a grafting method based on such properties, and thus fails to overcome the occurrence of gel formation and yellowish phenomenon which are fundamental disadvantages in the event of melt processing of polyvinyl alcohol.
Polyvinyl alcohol is known as having the most excellent barrier properties against gases and organic solvents among existing polymers. However, the facts that melting point is close to the thermal decomposition temperature and that the gel forms easily in processing prevents directly using the excellent barrier properties of polyvinyl alcohol. Such gel is difficult to melt evenly and this results in difficulties with processing into articles especially at the processing into a film. Therefore, even if it is processed into a film, the film is of poor quality and low marketability. Also, polyvinyl alcohol is heat-sensitive and the thermal decomposition occurs very easily. Such a thermal decomposition phenomenon shows as the above-explained increase of gel and yellowish phenomenon. Especially, the yellowish phenomenon precedes rapidly as the processing temperature increases. As a result, dark yellowish phenomenon may occur at a conventional polyolefin processing temperature, which deteriorates the marketability.
To solve the above mentioned problems, U.S. Pat. No. 3,148,202 discloses the introduction of a plasticizer but it did not completely solve the thermal decomposition as well as the gel formation. As a plasticizer, polyhydric alcohol or polyethylene oxide was added and plasticization was carried out to melt polyvinyl alcohol. However, when the amount of plasticizer used is small, its effect is insignificant. When the amount is large, the tackiness of final products increases and thus deteriorates the marketability. Therefore, such a method does not contribute to the solution against gel formation in final products.
On the other hand, other process including the use of water as a plasticizer was also attempted. According to the process, water lowered the melting point of polyvinyl alcohol. The perfect crystal was dispersed evenly to form a gel-free melt state, which was then processed into a casting film. The resulting casing film was processed into a sheet without water by way of drying moisture or extruded into a tubular film for biaxial stretching. However, the process has problems in that (1) the thickness of the film is limited by the speed of removing water, (2) the crystal is re-formed due to a slow drying step, and (3) the water-removing step needs a large amount of energy which in turn greatly increases the cost for manufacturing the film. In addition, the above mentioned water-based technique cannot be used in the coextruded structure of the film because it is practically impossible to remove water from the coextruded film. The technique also cannot be used in blow molding, Therefore, the use of a water-based technique is restricted to a narrow range.
For these reasons, extruded articles such as films, sheets and containers which were produced by coextruding polyamides, polyvinylidene dichiondes (PVDC) and ethylene vinyl alcohol copolymers (EVOH) having barrier properties against gases and organic solvents as well as better processability than polyvinyl alcohol with polyolefin were used conventionally. Although polyamide has better processability than polyvinyl alcohol, the polyamide has a problem in that its barrier properties against gases and organic solvents are poor and it needs special processing technique because it has difficulty when being processed into biaxially stretched films. Using PVDC is also greatly restricted for the reason that when products comprising PVDC are burnt, noxious gases are produced and they cause environmental problems. EVOH having excellent barrier properties is very difficult to polymerize because the control range of ethylene and vinyl alcohol composition is very narrow. The homopolymer of vinyl alcohol produced as a by-product in a polymerization, in particular, may grow into gel or appear as burn spots during extrusion. Therefore, the process for removing the homopolymer is indispensable, which makes EVOH resin very expensive. It is also very difficult to process it into a film.
It is, therefore, an object of the present invention to provide compositions with improved melt processability due to other added components while showing excellent barrier properties of polyvinyl alcohol against gases and organic solvents in a final processed article. The realization of the purpose is supported by the fact that the shape of cross section of a resin pellet obtained by melt-extruding the composition has a unique morphology such as the cross section of an onion.
It is another object of the present invention to manufacture films, sheets and processed articles having excellent barrier properties against gases and organic solvents from the composition by using a conventional melt processing method.
It is a further object of the present invention to provide a multi layer article having excellent barrier properties against gases and organic solvents by the combination of the above films, sheets and processed articles with other resins.
As one aspect of the invention, a polyolefin/polyvinyl alcohol composition is provided and it comprises:
(A) 1 to 80% by weight of polyolefin and 20 to 99% by weight of polyvinyl alcohol,
(B) based on 100% by weight of the polyolefin, 3 to 40% by weight of high molecular compatibilizer or 0.1 to 5% by weight of low molecular compatibilizer, and 0.01 to 0.5% by weight of initiator that causes the reaction between the compatibilizer and polyolefin, or the mixture of said high molecular compatibilizer, said low molecular compatibilizer and said initiator,
(C) 3 to 50% by weight of plasticizer based on 100% by weight of the polyvinyl alcohol,
(D) 1 to 10% by weight of processing aid based on 100% by weight of the polyvinyl alcohol, and
(E) 0.01 to 5% by weight of antioxidant based on 100% by weight of polyvinyl alcohol.
It is a further object of the present invention to provide films, sheets and processed articles manufactured by melting said composition and multi layer products using the same.
The other objects and features of the present invention will become apparent to those skilled in the art from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.